Good question, DMSO was used as a negative control that we could use as a sort of baseline comparison against our compounds. Ideally, we would want a negative control solely with Salmonella to have high absorbances after 24 hours, meaning that the Salmonella grew and did what it was supposed to, and the DMSO didn’t interfere with growth.
By “solubility issues”, we mean that when we tried to put our compounds Resveratrol and Trans-Resveratrol into solution (they came in powdered form), the compounds were not soluble in DMSO at higher concentrations, and we could see cloudiness and murkiness in the 96 well plates. This caused high absorbances when we read them in the spectrophotometer and high absorbances once again suggest more bacterial growth. Because of our problems with solubility of our compounds in DMSO, we couldn’t come to many conclusions about their antibiotic effects.
I think what you are referring to is the negative control bar, whose wells only contained DMSO and Salmonella so that the bacteria are able to grow and do their thing. The DMSO had a higher absorbance when it did what it was supposed to (in the Resveratrol graph for example) because it acted as a negative control (what we were hoping it would do). A negative control is something that the compound is suspended in and something that ideally doesn’t add or take away from the effect of the compound of interest. A positive control is something that is known to work, and in our case, we used ampicillin because it is an approved antibiotic.
Great question Kayla! Different strains of Salmonella have slight variances in their anatomy. For example, the difference between Salmonella Typhi and Salmonella Typhimurium is just the presence of an extra antigen called the Vi antigen on S. Typhi. I’m guessing this could cause differences in how the bacteria are able to get into cells or macrophages where they proliferate and worsen an infection. If and when we test on macrophages, it’d be interesting to see if one strain is able to get into the cell better or if the compound interacts with the bacteria any differently. We also know that Resveratrol might act via membrane depolarization and slight differences in what the antigens look like in different strains of Salmonella may lead to different outcomes as to how the compound interacts with the bacteria.
Another approach in drug discovery is to make the bacteria hyperpermeable to drugs so that screening of compounds comes more easily and some medicinal chemistry and altering of the compound can be done later!
curesymposium.org 
Why did you test the bacteria with DMSO? What do you mean when you say you had solubility issues?
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Good question, DMSO was used as a negative control that we could use as a sort of baseline comparison against our compounds. Ideally, we would want a negative control solely with Salmonella to have high absorbances after 24 hours, meaning that the Salmonella grew and did what it was supposed to, and the DMSO didn’t interfere with growth.
By “solubility issues”, we mean that when we tried to put our compounds Resveratrol and Trans-Resveratrol into solution (they came in powdered form), the compounds were not soluble in DMSO at higher concentrations, and we could see cloudiness and murkiness in the 96 well plates. This caused high absorbances when we read them in the spectrophotometer and high absorbances once again suggest more bacterial growth. Because of our problems with solubility of our compounds in DMSO, we couldn’t come to many conclusions about their antibiotic effects.
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Why did the DMSO have a higher absorbance?
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I think what you are referring to is the negative control bar, whose wells only contained DMSO and Salmonella so that the bacteria are able to grow and do their thing. The DMSO had a higher absorbance when it did what it was supposed to (in the Resveratrol graph for example) because it acted as a negative control (what we were hoping it would do). A negative control is something that the compound is suspended in and something that ideally doesn’t add or take away from the effect of the compound of interest. A positive control is something that is known to work, and in our case, we used ampicillin because it is an approved antibiotic.
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What sort of results would you expect to see if you tested different strains of salmonella? What in particular would be most likely to change?
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Great question Kayla! Different strains of Salmonella have slight variances in their anatomy. For example, the difference between Salmonella Typhi and Salmonella Typhimurium is just the presence of an extra antigen called the Vi antigen on S. Typhi. I’m guessing this could cause differences in how the bacteria are able to get into cells or macrophages where they proliferate and worsen an infection. If and when we test on macrophages, it’d be interesting to see if one strain is able to get into the cell better or if the compound interacts with the bacteria any differently. We also know that Resveratrol might act via membrane depolarization and slight differences in what the antigens look like in different strains of Salmonella may lead to different outcomes as to how the compound interacts with the bacteria.
Another approach in drug discovery is to make the bacteria hyperpermeable to drugs so that screening of compounds comes more easily and some medicinal chemistry and altering of the compound can be done later!
LikeLike